Purification of sugar juices



G. E. G. voN sTlETz PURIFICATION OF SUGAR JUICES Filed May 16, 1934 l.niv a.J ou T S51 Ewa@ @Eg I@ SM2, nous@ si l,5 -U I@ Re orive Time Fodor514 hi Mmmm? atented jan. L l2, 1937 lili* CATION OF SUGAR JUECESApplication May 16, 1934, Serial No. 725,894

11 Claims. (01.*127-48) This invention relates to the manufacture ofsugar, and particularly toimprovements in the carbonation process forpurifying Juices and syrups.

The disadvantages of the universally used carbonation processes havelong been recognized.

These include the use of excessive quantities of lime; the necessityfor'high juice temperatures to avoid ltration difliculties; the additionof sodium compounds which increase the losses of sugar as molasses; andinemciency of purification, particularly as regards removal of colloidalmaterial and residual calcium.

Many variations on the usual procedure such as the step-wise addition ofthe lime and the fractional removal of impurities under diierentconditions of alkalinity, as well as the use of supplementary reagents,including ammonia and its salts, have been suggested as improvements. In

spite of these disclosures, a commercially feasible process whichpermits full realization of the benents to be derived from suchprocedures has not heretofore been developed. This was inevitablebecause the optimum conditions of operation,

Particularly control of hydrogen ion concentration and temperature, hadnot previously been discovered.

In the following description of my invention and of a preferred methodof carrying it out, particular reference is made to the manufacture ofbeet sugar although the principles involved are equally applicable tokindred arts, such as cane sugar manufacture, by proper adjustment ofthe conditions to meet the well known differences in character of thejuices involved.

Sugar renners have recognized the fact that the degree of clarication isrelated, inversely, to the amount of residual calcium salts left in thejuice, provided the nal calcium oxide elimination takes place at theoptimum point pH 8.4 or

hydrogen ion concentration of 2.5x10-9.

In present processes alkali'metal compounds, e. g. soda aga, are used toreduce the nal calcium content of the juice, but the undesirability ofthe practice is universally admitted. Asit is impossible to remove thesecompounds in `later operations they increase the molasses losses. Theuse of ammonia has been suggested in this connection becauseitis'capable of subsequent removal.

, But it has not been applied successfully commercially .because offailure to properly control the hydrogen ion concentration andtemperature oftion is insuflicient to bring about a pronounced reductionin dissolved calcium. It is not only necessary to assure a certaindefinite ammonia alkalinity, but it is also necessary to have in thesolution suilcient suitable acid ions such as SO3= or preferablycarbonate ions obtained by carbonation to force the precipitation ofthe' residual calcium.

The ammonia used may advantageously be made the carrier of useful acidradicals which 10 form precipitates with lime possessing high sorptivecapacity. Under these conditions the ammonium salt is introduced as thefirst step in the clariflcation, although further amounts may be addedat later stages. In general the best results 15 are obtained byintroducing the ammonium salt before the addition of lime. By the mixingof the two reagents in solution a more rapid precipitation results thanis possible in the standard methods now in use. 'I'he precipitate formedis 20 more finely divided and a more effective 'sorptive agent. Thesulilte has been found exceptionally effective but the carbonate,oxalate, phosphates, tartrate, or other such salts may also be used.

For economic commercial application of this 25 invention a relativelylow temperature procedure of carbonation is to be preferred because ofthe ammonia losses which accompany any evaporation of the juice. Byoperating at relatively lower temperatures substantial heat economiesare 30 also possible. A further advantage to be derived from coldoperation, is a marked improvement in the sorption of colloidal materialby the precipitates formed. Carbonation at temperatures below 85 C. hasnever previously been practicable 35 because of the poor flltrability ofthe precipitates obtained. My procedure of control of hydrogen ionconcentration, however, permits these operations to be carriedout atmuch lower temperatures than 85 C. I can successfully operateat 40temperatures as low as to 65 C.

This is made possible by the discovery of the possibility of arrivingata zone of clarication and rapid settling in the hydrogen ionconcentration range of 3x109to 10-10 or pH range of 45 8.5 to 10.0 bycarbonating the limed sugar juice beyond the first zone of goodsettling; which usually occurs at about the hydrogen ion concentration 51011 to 2x10-12 (pH 10.7 to 11.2). In this zone of hydrogen ionconcentration 3x10-g 50 to 10-10 the juices are of a red-brown colorinstead of the usual light yellow. They have been termed burnt uices.when inadvertently encountered in the industry and have been studiouslyavoided from fear of their darker color. I 55 bonation which follows.

however, because it is readily eliminated in the subsequent steps cf myprocess. f

By first eliminating a part of the impurities in the zone of rapidsettling where the pH=8.5 to 10 (hydrogen ion concentration 3X109 tol01) a. relatively small compact mud of comparatively high organiccontent is obtained. Because of its small amount, this precipitate canbe of poor filtrability without reducing factory capacity below that ofexisting processes, even when the operations are carried out at lowtemperatures. vThis is in no way possible with any other process whichhas been suggested, for all involve as an essential feature the removalof the first impurities in a bulky precipitate representing anappreciable proportion of all the muds which have to be filtered.

Due to the fact that most of the disturbing organic substances will havebeen eliminated by this pre-carbonation treatment, filtration. withoutsettling is practicable after the main car- In this step the impuritiesare removed at a lower hydrogen ion concentration than in the rsttreatment. Again due to the previous removal of colloidal material, amore efficient sorption of that remaining is possible as the operationscan be carried out nearer the true iso-electric point of such materialas remains.

In the following description of a preferred method of carrying out myinvention as applied to beet sugar manufacture, it will be understoodthat the well known variations in the character of the beets sliced willrequire corresponding variations in the quantities of reagents used andin the conditions of operation. This applies particularly to thehydrogen ion concentrations Y specified, it being recognized in presentpractice that the optimum may vary widely as from a hydrogen ionconcentration of 6 X 10-11 to 6X 10-12 (or pH 10.8 to 11.8) during thesame campaign and even more for differenty campaign years.

According to my invention, raw diffusion juiceat about to 65 C. istreatedwith about 0.1% ammonium sulte (all quantities of reagents willbe expressed as percentages of the juice weight) followed by theaddition of about 0.4% calcium oxide as milk of lime (or as calciumsaccharate when' operating in conjunction with the Steffen process). Theresulting mixture, having a hydrogen ion concentration of about 10"11 to10-12 or a pH value of about 11.0 to 12.0 is brought by carbonation inthe usual way to a hydrogen ion concentration of about 3x109 to 3 101 ora. pH of about 8.5 to 9.5, preferably more than a hydrogen ionconcentration of 10-9 (pH 9). The resulting precipitate is settled,preferably in the Dorr thickener commonly employed for the rst stage ofseparation in continuousA methods of operation, and then filtered. Thetemperature during filtration need not be higher, than 65 C. If desired,small quantities of lime, about 0.01- 0.02%, may be added to the mudtoffacilitate filtration. y

To the clear juice from the settling tank (Dorr overflow) about 0.05%(NHDaSOs is added followed by about 0.4% CaO and the mixture carbonatedin the usual way to a hydrogen ion concentration of about 3 10n to10-12' or a` pH of about 10.5 to 12.0, preferably a hydrogen ionconcentration between V3 10L2 to 10--12y after ltration withoutsettling, the carbonation of the filtrate is continued to a hydrogen ionconcentration of about 10-8 to 2X109 or a pH value of about 8.0 to 8.2.The alkalinity of the juice may unfiltered juice may be heated in theusual open boilers until this hydrogen ion concentration is.

attained as the result of the more rapid evolution of CO2 as comparedwith NH3. In either case, a time interval at the lower hydrogen ionconcentration of at least 10 minutes should be provided to allow anopportunity for the completion of'precipitation before filtration.

The purified juice is then treated by the usual processes for recoveryof the sugar.

When the ammonia content of th'e clarified thin juice is below 0.070%where the juice has a hydrogen ion concentration less than 3X 10-9 thereis no danger of appreciable corrosion of copper and brass apparatus orfittings. `Where higher hydrogen ion lconcentrations are present evengreater amounts of ammonia may be present without causing corrosiondifiiculties. It is not desirable, however, to allow the clariiied thinjuice to reach a hydrogen ion concentration higher than 10-a as thesubsequent elimination of ammonia thezbecomes difficult. It is to benoted that the total amount of ammonium sulte used in the abovedescribed illustration of an application of my process, represents onlyabout 0.045% ammonia or far below the amounts which produce corrosion.

By the use of automatic control apparatus of the hydrogen ionconcentration of the juices, my invention may be carriedout withoutpermitting the alkalinity of the y.juices to materially exceed. duringany one step of the operations, that at which the precipitatedimpurities are to be removed.

.Both methods of operation are indicated dial grammatically in thedrawing, wherein Figure 1 represents a How-sheet of' my process ascarried out in batch operation, and Figure 2 a ow-sheet of theoperations as carried out by continuous methods with automatic controlof the pH value of the juices. s

The relative time factor denoted in these figures is intended merely toshow the order of the operations. The widths of the plateaus indicatingiiltration, for example, are not, in any sense, measures of the timerequired for these operations as compared with the other steps in theprocess.

The order of the various operations is designated by the labels andtheir effect on the pH value of the juice is indicated by the scaleshown. The particular points used in the drawing are onlyrepresentations of the pH ranges previously defined for the steps towhich they refer. In Figure l no definite pH value has been assigned tothe juice` after the second addition of ammonium sulfite and limebecause this may be varied widely by the use of different amounts ofthose reagents.

The present invention accordingly provides a practical commerciallyvavailable process for pur- A ifying sugar juices which obviates thedifficulties eration of thejui during clarification in the zone g5 `tionare improved and the difdculties of foaming reduced. v

The introduction of (NH4)2SO3 at the beginning of the clarificationproduces juices and sugars of greatly improved color. Another importantfeature of my invention is the presenceA of ammonium sulte at eachseparation stage up to the evaporation stage.A This results in greatlyimproved precipitation and in the formation of precipitates of increasedsorptive capacity, settling rate and ltrability.

The thorough removal of calcium in the final stage of treatment resultsin juices which not only form no scale in the evaporators and heaters,but actually have been observed to dissolve'the scale left in theapparatus by juices purified in the usual way. Moreover, this.elimination of calcium results in lower sugar losses because lessmolasses is produced.

Some of the advantages of my process over the i standard procedure ofdouble carbonation Jand sulfur dioxide saturation are shown by thefollowing results determined during various factory and small scaletests of my method. l

. Standard Improved procedure process Consumption oi CaO as milk oi limeas l percent oi iuice weight 2. 12 l. 64 Consumption oi soda ash aspercent oi juice weight 0. l None Consumption ot sulfur as percent oijuice weight 0. 07 Nono Consumption of ammonium sulte as percent oljuice weight.. None 0. 12 Purity oi clarified juice; 90. 9 92. 4 CaOcontent of clarided juice as grams per f 100 Brix 0.084 0. 010 Color oiclarified juice (pure water as zero) (lproduct oi standard ocedurens,100) 100 78 Su fur content oi du sugar as suliite parts per 1,000,0000. 30 2. 33 ,f Color oi final sugar (scale pure water=0). f 11 9 Myinvention is'capable of many modications. Where it may seem desirablenot Ito make changes in equipment already installed .or for otherreasons the nrst step described above of removal of impurities in the-range of hydrogen ion concendetail the preferred embodiment of myinvention and some variants thereof, it will be understood that this isonly for. the purpose` of making the invention more clear and thattheinvention is not to be regarded as limited to the details of operationdescribed, nor is it dependent upon the soundness or accuracy of thetheories which I have advanced as to the advantageous results attained.On the other hand, the invention is to be regarded as limited only bythe terms of the accompanying claims, in which it is my intention toclaim all novelty inherent therein asl broadly as is possible in View ofthe prior art.

I claim as my, invention:

l. A method of purifying sugar solutions from which the bulk of theprecipitable material has beenl removed, comprising carbonating thesolution to a hydrogen ion concentration within the` `range 2X 1 0-9 toi0-8 and adding ammonia thereto to reduce the hydrogen ion concentrationthereof to a value within the range of 3x10-9 to lil-1 and subsequentlyremoving the resulting precipitate.

l2. A method of purifying sugar solutions prior to evaporation thereofcomprising introducing at least one basic agent comprising free ammoniato bring the hydrogen ion concentration of said solution `to a value notgreater than about -a while containing an ammonia concentration notgreater than 0.07% and then evaporating said solution whereby scaleformation in 'the vaporator and corrosion of copper-containing equipmentis`substantial1y avoided.

3. A method vofpurifying sugar solutions comprising as the first stepthe separation of precipitated impurities by carbonating the limedsolutin to a hydrogen ,ion concentration between 3X109. and 3 10-1, thenliming and carbonatprising valkalinizing the solution then acidifying toa hydrogen ion concentration of about 3x10-V9 to 3X 101 removing theresulting precipitate and subsequently separating further impurities bytreatment with alkaline and acid electrolytes to bring the hydrogen ionconcentration first within the' range 5 1O-`11 to 10l12 and subsequentlywithin the range 3X109 to 3X10,1. 5. A method of purifying sugarsolutions from which the bulk of the precipitable'material has beenremoved by acidifying the alkaline solution to a hydrogen ionconcentration of about 5X 10-11 to l0 12 comprising the adiustment ofthe hydrogen ion concentration thereof by treatment with Y acid andalkaline electrolytes to a point within the range 10Ta to 2X10-9, thenreduction of the hydrogen ion concentration before removal of impuritiesis effected toa point within the range 3 X 10'*9 t0 3 X 10-10.

6. A method of purifying sugarlsolutio'ns from which the bulk of theprecipitable material has been removed by acidifying the alkalinesolution to a hydrogen ion concentration of about 5X 10"l1 to 10,lcomprising carbonating the solution in the presence of an ammonium saltto a hydrogen ion concentration of about'lOa to 2x10, thenI heating thesolution to remove carbon dioxide therefrom and reduce the hydrogen ionconcentration to a valueof about 3X109 to 3X101.

7. A method of purifying sugar solutions coinprising as the rst stepcarbonating the limed so- Alution in the presence of an ammonium salt ata temperature below 85 C. to a hydrogen ion con-. centration of about3X109 to 3X101 whereat Y precipitable material iscaused to settle out,liming effecting a iinal removal of impurities at a hydrogen ionconcentration o f about 3 10-9 to 3 10-10.

8. A method of purifying sugar juices wherein the juice has been treatedso as to be strongly alkaline, which comprises carbonating the juice toa hydrogen ion concentration of about 3X 10-9 to 3X 10-10, whereat rapidsettling of precipitable material takes place, ltering, stronglyalkalinizing the ltrate and carbonating to a hydrogen ion concentrationof -about 5 10-11 to 10-12, again removing precipitated material andacidifying and eiecting a third separation of impurities at a hydrogenion concentration of about 3 109 to 3X101.

9. A method of purifying sugar solutions com-v prising treating thealkaline solution with an acid electrolyte in the presence of anammonium salt aoezaee prising carbonating alkalinized juice to ahydrogen ion concentration of about 3x10-s to 3X 10-10, removing thematerial precipitated thereby, alkalinizing and carbonating thepartially puried juice to a hydrogen ion concentration of about 5X 10-11to 1012, removing further precipitated material, carbonating to ahydrogen ion concentration of about 10*8 to 2X 10-9 and subsequentlylowering the hydrogen ion concentration to about .3x 10-9 to 3X 10-1obefore nal removal of impurities.

11. A method of purifying sugar solutions comprising treating thesolution with ammonium suliite and alkaline and acid electrolytes tobring the hydrogen ibnA concentration of the alkaline solution irst toabout 3X 10V-9 to 3X 10-10 and then to about 5x 1li-11 to 10-12,removing precipitated impurities in each'of said hydrogen ionconcentration ranges, acidifying the resulting solution to a hydrogenion Y concentration of about 10-8 to 2x10-9 and subsequently loweringthe hydrogen ion concentration to about 3X 10-9 to 3X 10-1o before finalremoval of impurities.

GEORGE E. G. VON STIETZ.

